1. Field of the Invention
This application relates to a process for the preparation of nitrophenylalkanols, and to the compounds thus prepared.
2. Description of the Prior Art
There exists an interest in the preparation of nitrophenylalkanols, since these compounds are useful intermediates in the production of other chemical compounds such as indole or 3-methylindole (cf. DT 2328330), herbicidal urea derivatives (cf. GB No. 8,218,455), or nitrostilbenes.
It is known to prepare the above-mentioned compounds by the addition of nitrotoluenes to aldehydes according to the following scheme: EQU RCH.sub.3 +R'CHO.fwdarw.RCH.sub.2 --CHOHR'
R represents herein a nitrophenyl group, which may be further substituted, and R'CHO represents an aliphatic or aromatic aldehyde, which aldehyde preferably does not have alphahydrogen atoms. By adding more aldehyde to the reaction mixture, further addition to yield nitrophenylalkanediols and/or -triols occurs. For the purpose of this application, alkanediols and alkanetriols are included in the broad class of alkanols. As catalyst a strong base like hydroxide or alkoxide dissolved in a polar, aprotic solvent has to be used [J. Bakke, Acta Chem. Scand. 21, 7 (1967) 1967-8]. The yields of this reaction are low, however, the more so because a Canizzaro-reaction of the aldehyde is competing. Similar reactions have been described in unexamined Japanese patent application Nos. 77.108941, 77.122330, 77.139035 and 77.156825 using various combinations of catalysts and solvents, in particular phase transfer catalysts, and in German Offenlegungsschrift No. 3020236, using special solvents and molar ratios of the reactants. Disadvantages of all these processes are the unsatisfactory yields and selectivities and/or the rather complicated working-up of the reaction products because homogeneous catalysts are used.